Skeletal disorders that result from degenerative processes, such as arthritis, trauma, bone fracture, torn ligaments or tendons and congenital defects, are very common and have a great impact on patient morbidity, and health care costs in terms of days lost from work and patient hospitalization.
Various methods and materials for regenerating tissues have been developed to repair or restructure damaged or malformed connective tissues. Heretofore, however, conventional methods and materials have proven unsatisfactory for use in connecting soft tissues, such as tendons, ligaments, intervertebral disc articular cartilage and fibrocartilage to hard tissues such as bone or dentin.
Conventional methods of repairing hard connective tissues that require replacement. ie. bone, typically involves cutting or removing part or the damaged bone and then replacing the removed portion with an implanted matrix along which bone tissues will grow.
Known matrices used in bone repair have been constructed from a variety of materials including ceramics, metals such as titanium alloys, stainless steel, as well as various biodegradable polymers and composites. One known matrix disclosed in U.S. Pat. No. 5,108,755 to Daniels et al is formed from a degradable composite made up of a biodegradable polymer which is reinforced with loose or woven calcium sodium metaphosphate fibers as reinforcements. The biodegradable matrix is selected from poly(ortho ester), poly(lactic acid) and poly(glycolic acid) materials with the reinforcements made from fibers described in U.S. Pat. No. 4,346,028 which issued Aug. 24, 1982. As noted in Guo, W. et al in Calcium Polyphosphate Fibers for Composite Biomaterials--Degradation Studies, The 20th Annual Meeting of the Society for Biomaterials, Boston, Mass., April 1994, resorbable biomaterials having fibrous reinforcements may not be suitable for all applications. In particular, Guo suggests that calcium polyphosphate fiber reinforced composites may be susceptible to premature loss in strength and stiffness properties as a result of fiber degradation
Ceramic implants made from a synthetic hydroxyapatite (Ca.sub.3 (PO.sub.4).sub.3 OH), have been proposed by Nelson et al in Evaluation of New High-Performance Calcium Polyphosphate Bioceramics as Bone Graft Materials, J. Oral Maxillofac Surg., 1363-1371, 1993. Hydroxyapatite has, however, proven exceptionally slow to degrade in the body and therefore not generally considered to be a suitable biodegradable material. Ceramic implants of tricalcium phosphate have also been proposed, however, these implants have been found to have rates of degradation which are too fast.
Conventional methods of repairing and reattaching soft connective tissues, such as ligaments, tendons and cartilage to bone, typically involve driving a metal pin, staple, braid or other mechanical type fastener through the soft tissues and into a patient's bone to secure a portion of the soft tissue in place. A major disadvantage of conventional methods of reattaching soft tissues to hard issues exists in that there are physical limitations as to where such conventional mechanical fasteners may be used. The use of pins, staples and the like, frequently necessitates the stretching, bending or otherwise altering the natural positioning and configuration of the soft tissue so that it is positioned at the point of reattachment. The result is therefore that soft tissues which become detached from the bone may be reattached at a location distant from the original point of natural hard tissue/soft tissue attachment. In addition, soft tissues connected by mechanical fasteners do not reattach biologically to the bone and are weakened at the site of attachment.
The possibility of reintroducing regenerated articular cartilage into a joint to replace or repair damaged cartilage is disclosed in U.S. Pat. No. 5,326,357 to Kandel, which issued Jul. 5, 1994. U.S. Pat. No. 5,326,357 describes a process by which in vitro grown cartilage is removed from a synthetic substrate prior to implantation. While reintroduced articular cartilage may permit further articular cartilage growth, Kandel fails to achieve a method or structure by which such articular cartilage may be securely reattached to a specified and preferred bone site.